TCAD Sentaurus–IC WorkBench EV Plus Interface
1. Working with the GUI

1.1 Strategy
1.2 Starting the ICWBEV Plus GUI
1.3 Renaming Layers
1.4 Creating Auxiliary Layers
1.5 Using Boolean Operations
1.6 Using Stretches
1.7 Defining Simulation Domains
1.8 Saving Information

Objectives

• To start the GUI and perform basic operations in the TCAD Sentaurus–IC WorkBench EV Plus (ICWBEV Plus) interface.

1.1 Strategy

Sentaurus Process does not use the GDS layout file directly. The layout information must be prepared in a special way, and you must declare the simulation domains. Additional information that makes the process simulation setup more convenient can be supplied. In this module, the following strategy is applied:

• The GDS file is loaded into the graphical user interface (GUI). A mapping of layer numbers to layer names is performed and is saved for later use.
• Auxiliary layers are defined.
• Simulation domains are defined.
• Information is saved.

The complete project can be investigated from within Sentaurus Workbench in the directory Applications_Library/GettingStarted/ic/icwb_for_process.

1.2 Starting the ICWBEV Plus GUI

To start the GUI in a mode that allows generating information for TCAD Sentaurus, an environment variable must be set. In a Linux cshell, this can be performed on the command line or in the .cshrc file:

setenv ICWBEV_USER SENTAURUS

Then, the GUI can be started from the command line with:

icwbev

A GDS file can be loaded by selecting File > Load. An example is shown in Figure 1.

A detailed description of ICWBEV Plus functionality is available by selecting Help > Topics. In this document, only functionality relating to layout information in process simulation is discussed.

Figure 1. Main window of ICWBEV Plus, with a GDS file loaded. (Click image for full-size view.)

1.3 Renaming Layers

The original GDS file contains numbered layout layers. For a TCAD simulation, this is not very convenient, and most users want to address layers by names. The mapping of layer numbers is performed by clicking into the window with the layout layers and adding the corresponding name, as shown in Figure 2.

Figure 2. (Left) Numbered layers and (right) renamed layers. (Click images for full-size views.)

The mapping of layer numbers to layer names must be saved. To save the mapping:

1. Click the Save Sentaurus Markup File toolbar button .
   The Save Sentaurus Markup File dialog box is displayed.
2. Select the Active layout option.
3. In the Save file as field, enter the name of the file.
4. Click OK.

It is convenient to save the file with a .tcl or .mac extension because these are predefined file filters when reading or writing files in ICWBEV Plus. The file that is saved this way is an ASCII file, which looks like:

# Sentaurus markup information - Wed Mar  7 16:23:00 CET 2012
# version - D-2010.06-12.284183 (Production)
default winding 1
layout open BICMOSinverter.gds Inverter
cell transform 1.0 0.0 0 0.0 0.0
layer add 1:0
layer configure 1:0 -name NWELL -fill #00ff00 -pattern fill12-a 
  -outline #00ff00 -lineStyle solid -lineWidth 1 
layer add 2:0
layer configure 2:0 -name NPDIFF -fill #0000ff -pattern fill12-b 
  -outline #0000ff -lineStyle solid -lineWidth 1 

This file contains the absolute path to the original GDS file and the mapping of layer numbers to layer names. Therefore, you can read this file into the ICWBEV GUI instead of loading the GDS file. In many cases, however, the correspondence of layer numbers to layer names is the same for many GDS files. You can delete the first lines of this file (until cell transform) and keep only the lines starting with layer configure. Then, this file can be read after a GDS file has been loaded into the ICWBEV Plus GUI. Finally, a file containing the layer numbers and the corresponding layer names can be created manually; the display options can be omitted:

layer configure 1:0 -name NWELL
layer configure 2:0 -name NPDIFF

1.4 Creating Auxiliary Layers

In a TCAD simulation flow, it is often helpful to create additional layers and to use these as masks. A GDS file usually has layers for metallization, but these layers do not distinguish between different contacts such as source, gate, and drain. In a TCAD simulation, however, it is essential to have that information.

To add this information to the layout, auxiliary layers containing several polygons can be added. A new layer is added by selecting Layout > New Layer. A layer number and a layer name must be assigned, and a fill pattern and a color for the polygons can be selected. Polygons can be drawn by selecting the Shape toolbar button.

Figure 3 shows the part of a layout that contains an NMOS transistor. Three new layers have been added: nsource, ngate, and ndrain. With this, contacts can be assigned easily in Sentaurus Process, and no changes are necessary if a different simulation domain is chosen.

Figure 3. Introducing auxiliary layers: NMOS part of a layout is shown, and additional layers are introduced for the source, drain, and gate contacts. (Click image for full-size view.)

It is not necessary that these additional polygons are defined everywhere in the layout (as in the example above, it is not necessary to create polygons for all contacts in the layout). It is only necessary to define them in the regions in which TCAD simulations are performed (the TCAD simulation domains).

1.5 Using Boolean Operations

ICWBEV Plus supports the use of Boolean operations. This can be helpful when creating auxiliary layers, for example. To apply Boolean operations, the cell must have an alias. The Boolean operations must be typed in the Command pane of the GUI. With the commands:

cell alias a
bool a30= a5+a9

the cell acquires an alias (a), then a new layer (30) is created that is the logical OR of layers 5 and 9. More detailed information about the use of Booleans can be found in the ICWBEV Plus tutorial (Help > Topics, then select the tutorial from the available documents).

The layout must be flat to allow for Boolean operations. If the layout is hierarchical, type hierarchy explode in the Command pane of the GUI.

1.6 Using Stretches

ICWBEV Plus supports the use of stretches. A stretch is a line in the layout perpendicular to which the layout can be stretched.

Such a stretch is introduced by clicking the Stretch toolbar button and drawing a horizontal or vertical stretch line in the layout (see Figure 6). The stretch is named automatically. It can be renamed in the list of open cells (see Figure 5). The exact coordinates can be specified there as well.

The stretch utility applies the stretch to all mask layers. The effect is illustrated in Figure 5 in which a gate length variation is simulated. If you want to apply a stretch only to one layer, see Section 2.1 Defining the Process Simulation Domain.

Figure 4. Part of a layout showing a stretch; white arrow indicates the positive direction of stretch values. (Click image for full-size view.)

Figure 5. Parameterizing a simulation using a stretch that is applied to the middle of the gate mask. (Left) With a stretch value of 0.0, the original mask is used. (Right) With a stretch value of 1.0, all mask edges with a coordinate right of the middle of the gate are moved by 1.0 μm. (Click images for full-size views.)

1.7 Defining Simulation Domains

You can define 1D, 2D, and 3D TCAD simulation domains. They are called point, gauge, and highlight, respectively, and can be drawn into the layout by selecting the appropriate button from the toolbar:

• for point
• for gauge
• for highlight

In most cases, you will draw the simulation domains at their approximate positions, the exact coordinates can be specified in the list of open cells (see Figure 6). The names of the simulation domains also can be changed there.

It is recommended not to let simulation domains coincide with mask edges.

Figure 6. Part of a layout with several simulation domains: the exact coordinates and the names of the simulation domains and stretch lines can be specified in the list of open cells in the left pane. (Click image for full-size view.)

1.8 Saving Information

After all the steps described in the previous sections, two files should be saved: one file that contains all of the above information and can be used for a restart at this step, and one file that can be used with Sentaurus Process.

The first file is saved with the Save Sentaurus Markups toolbar button (). This file contains the mapping of layer numbers to layer names, the auxiliary layers, and the TCAD simulation domains. The name of the original layout file and the absolute path to it are saved in this markup file, so it is sufficient to load only this file if changes need to be made.

The second file is saved with the Generate Sentaurus Info toolbar button (). This file contains the mapping of layer numbers to layer names, and the layers inside TCAD simulation domains.

When writing a file with Generate Sentaurus Info, ICWBEV Plus extracts polygons into the TCAD layout. The polygons are extracted as they are. "Strange" polygons, such as self-intersecting polygons, may create problems in Sentaurus Process. You can instruct ICWBEV Plus to perform a cleanup operation during the process of extracting the TCAD layout file. In most cases, this leads to regular polygons in the TCAD layout file.

To activate this clean up option, enter:

set sentaurus::do_bool 1

in the Command pane of ICWBEV Plus. Starting with ICWBEV Plus Version G-2012.06, you can activate the cleanup option from the Save Layout Information for Sentaurus dialog box by selecting the Merge Shapes in Sim3D regions option.

It is recommended to save both files and to name the files according to their content, for example, *_mkp.mac for the markup file, and *_lyt.mac for the layout file to be used in Sentaurus Process.

You can reload and edit the markup file (*_mkp.mac) as needed. The TCAD layout file (*_lyt.mac), however, should be reloaded for viewing only (for example, for debugging purposes). Editing and resaving the TCAD layout will result in duplication of polygons.

Since the markup file contains the full path to the GDSII file, you will need to edit the markup file if you move the GDSII file or you rename the directory containing the markup file.